1. Field of the Invention
The present invention relates to a scanning type image display optical system comprising an optical scanning unit which forms a two-dimensional image by light scanning and a scanning type image display apparatus.
2. Description of the Related Art
With the advancement in the performance of the semiconductor technology, the data communications environment has also become more sophisticated, and portable information terminals have progressed rapidly. In such a situation, an ever-greater advanced display of information by portable information terminals has been demanded, and an improvement in display resolution of portable information terminals has been demanded, therefore, head mounted displays (HMDs) have come to receive great attention.
Most of the current HMDs are constructed such that a transmission type liquid crystal display is used as an image display element and images displayed on the liquid crystal display are observed by an observer as a virtual image through an ocular optical system.
A transmission type liquid crystal display is illuminated by a back illuminating optical system such as a fluorescent tube, however, transmittance of the liquid crystal display is on the order of several percent and utilization efficiency of light is very low. Therefore, power consumption is great and for use as a display unit of a portable information terminal, utilization efficiency of light must be improved.
On the other hand, techniques relating to a display apparatus using no such two-dimensional image display element as a liquid crystal display have been disclosed and suggested in U.S. Pat. No. 5,467,104, Japanese Laid-Open Patent Publication No. 2000-111829, etc. U.S. Pat. No. 5,467,104 has disclosed a technique for forming an image directly on a retina via an optical system by scanning of R (red), G (green), and B (blue) light in the horizontal direction and vertical direction.
In addition, in Japanese Laid-Open Patent Publication No. 2000-111829, a scanning type image display apparatus which uses a beam from a beam source for two-dimensional scanning and leads the beam into an eyeball via an integrated reflecting member disposed in front of the wearer's (observer's) eye.
However, in the scanning type image display apparatus disclosed in the above U.S. Pat. No. 5,467,104, since it is required that light scanning is performed at a very high speed, a very small-sized device is used for a light scanning part constituted by a mirror or the like. Accordingly, a beam used for scanning becomes extremely thin, thus the diameter of the beam at the observer's pupil position becomes very small.
As a method for expanding such a small exit pupil diameter, techniques disclosed in U.S. Pat. No. 5,701,132 and U.S. Pat. No. 5,757,544 exist. In U.S. Pat. No. 5,701,132, by transmitting a scanning beam which has formed an intermediate image having a curvature through expanding members such as a lens array and a diffusion plate, the divergence angle of rays after transmission through the expanding member is expanded.
In addition, in U.S. Pat. No. 5,757,544, although this image display apparatus is not a scanning type, by transmitting, through a diffusing plate, light after being made incident into an image display element such as an LCD (liquid crystal display) illuminated by parallel light rays, the exit pupil is similarly expanded.
However, in these constructions disclosed in US patents, since the transmission-type exit pupil expanding members are used, the optical path becomes long, resulting in a large-sized apparatus.